A. Field of the Invention
The present invention relates generally to the communications field, and, more particularly to a system for removing a uniform length of a coating from a fiber optic cable.
B. Description of the Related Art
Along with the increasing prominence of the Internet has come the wide-ranging demand for increased communications capabilities, including more channels and greater bandwidth per channel. Optical media, such as fiber optic cables, promise an economical alternative to electrical conductors for high-bandwidth long-distance communications. A typical fiber optic cable includes a silica core (glass optical fiber), a silica cladding, and a protective coating. The glass optical fiber of fiber optic cables has a very small diameter, which is susceptible to external influences such as mechanical stress and environmental conditions. The index of refraction of the core is higher than the index of refraction of the cladding to promote internal reflection of light propagating down the core.
Certain uses of fiber optic cables require that a portion of the coating be removed from an end of the fiber optic cable or a portion of the fiber optic cable that is remote from the ends. For example, to make a fiber optic coupler, the coating is stripped from portions of at least two fiber optic cables, and the stripped portions are fused together in side-by-side relationship and stretched. It is important that the stripped portions of the fiber optic cables do not become weakened during the stripping process since weakened fiber optic cables can fail during subsequent process steps or during handling of the coupler when tensile stress is applied to the exposed glass optical fiber.
Other uses of fiber optic cables require that a portion of the coating, remote from the ends of the fiber optic cable, be removed. For example, when an optical fiber diffraction grating is provided in a fiber optic cable, a portion of the coating, remote from the ends of the cable, is removed. Ideally, the portion of the coating that is removed for provision of the diffraction grating should be consistent for all fiber optic cables, so that the removed portions of fiber optic cables may be properly recoated after the diffraction grating is etched.
While there are many methods for establishing a diffraction grating within a fiber, one method involves exposing photosensitive glass optical fiber to patterned light, via lasers. The lasers are used to etch lines in the glass optical fiber that is exposed (i.e., the coating removed) at the portion of the fiber optic cable remote from the ends of the fiber optic cable.
A coating of a fiber optic cable may be removed or stripped in a variety of ways. Coatings can be mechanically stripped from an optical fiber by placing the fiber within a hand-held tool, bringing blades of the tool into contact with opposite sides of the coating layer, and then moving the tool relative to the axis of the coated optical fiber. The bare portion of the fiber usually needs to be wiped with a cloth wetted with alcohol or the like to remove smudges and/or particles of coating that have been deposited on the bare portion of optical fiber by the coating removal process. This type of coating removal process has been built into equipment that performs the tasks of the technician, whereby the process is no longer manual.
These processes have various disadvantages. Processes that are adapted to remove coating only from the end of a coated fiber are often not useful for removing coating from regions remote from the fiber ends, a requirement for making diffraction gratings. Mechanical strippers can cause scoring or scratching of the fiber surface. For example, the fiber surface can be scratched as the bare glass fiber without its coating is removed from the mechanical stripping device. Some stripping methods do not result in a clean demarcation between the stripped coating and the coating remaining on the fiber. If the stripping process results in a ragged or uneven coating termination, the resultant stripped fiber may not be useful for its intended purpose. The wiping step to remove contaminants from a stripped fiber can cause more damage to the fiber than the mechanical stripping step. Finally, mechanical stripping that is manually performed is highly operator dependent as it is typically performed with a hand held stripper.
Coatings may also be chemically removed by contacting the coated fiber with materials such as sulfuric acid and hydrogen peroxide (to remove a polyester coating) or with sulfuric acid (to dissolve a polysyloxine coating). The primary chemical method for removing an optical fiber""s polymer coating with minimal degradation in tensile strength is acid stripping using a hot sulfuric nitric mixture, that is, 95% sulfuric acid and 5% nitric acid. Specifically, this method involves heating the sulfuric nitric mixture to approximately 185xc2x0 C., immersing the optical fiber in the hot sulfuric nitric mixture for approximately 20 seconds, and rinsing the optical fiber for two to ten seconds in a rinser, such as acetone, alcohol, methanol, purified water, or a combination of these.
Although tensile strength degradation is minimized, chemical stripping processes can be disadvantageous in that they are difficult to control, and may leave contaminants or residual coating on the fiber surface. Chemical stripping can also be disadvantageous in that it utilizes dangerous caustic chemicals that need to be safely handled and disposed of. Thus, safety concerns are often present with acid stripping methods. Field technicians employing acid stripping methods require well-ventilated areas, such as laboratory environments with exhaust hoods, and protective gear to safeguard themselves from fumes and burns associated with acids.
Furthermore, with current chemical and mechanical stripping systems, it is extremely difficult, if not impossible, to strip a consistent portion of the fiber optic cable coating. As discussed above, such consistently stripped portions are necessary if the stripped portions are to be properly recoated.
Thus, there is a need in the art to provide an apparatus for removing a consistent portion of a coating from a fiber optic cable in a safe manner, while minimizing the tensile strength degradation of the exposed glass optical fiber of the fiber optic cable.
The present invention solves the problems of the related art by providing a system and method for removing a predetermined length of coating from a fiber optic cable in a safe manner, while minimizing the tensile strength degradation of the exposed glass optical fiber of the cable.
In accordance with the purpose of the invention, as embodied and broadly described herein, the invention comprises an apparatus for holding a fiber optic cable to be stripped, including: a mount having means for retaining portions of the fiber optic cable; a push rod movably extending through said mount; and a fiber optic cable loop former connected to said push rod, wherein said fiber optic cable loop former is pushed away from said mount by said push rod and engages the fiber optic cable to form a loop therein.
Further in accordance with the purpose of the invention, as embodied and broadly described herein, the invention comprises a system for removing a predetermined length of coating from a fiber optic cable, including: a chemical bath; and an apparatus for holding a fiber optic cable to be stripped, having: a vertical column, a slide arm having a guide collar portion slidably provided on the vertical column, and a distal portion extending away from and integral with the guide collar portion, a mount extending from and connected to the distal portion of the slide arm, the mount having means for retaining portions of the fiber optic cable, a push rod movably extending through the mount, a fiber optic cable loop former connected to the push rod, wherein the fiber optic cable loop former is pushed away from the mount by the push rod and engages the fiber optic cable to form a loop therein; wherein the slide arm is lowered on the vertical column a predetermined height so that the loop formed in the fiber optic cable is provided in said chemical bath to remove a predetermined length of coating from the fiber optic cable.
Still further in accordance with the purpose of the invention, as embodied and broadly described herein, the invention comprises a method for forming a loop in a fiber optic cable so that a predetermined length of coating of the fiber optic cable may be removed in an apparatus having a mount with means for retaining portions of the fiber optic cable, a push rod movably extending through the mount, and a fiber optic cable loop former connected to the push rod, including: forcing the push rod downward to move the fiber optic cable loop former downward; retaining portions of the fiber optic cable against the mount and the fiber optic cable loop former with the retaining means of the mount to form a loop in the fiber optic cable; forcing the push rod upward, while the loop formed in the fiber optic cable is maintained.
Still even further in accordance with the purpose of the invention, as embodied and broadly described herein, the invention comprises a method for removing a predetermined length of coating from a fiber optic cable in a system having a chemical bath and a system for forming a loop in a fiber optic cable, the loop forming system having a vertical column, a slide arm having a guide collar portion slidably provided on the vertical column, and a distal portion extending away from and integral with the guide collar portion, a mount extending from and connected to the distal portion of the slide arm, the mount having means for retaining portions of the fiber optic cable, a push rod movably extending through the mount, and a fiber optic cable loop former connected to the push rod, including: forcing the push rod downward to move the fiber optic cable loop former downward; retaining portions of the fiber optic cable against the mount and the fiber optic cable loop former with the retaining means of the mount to form a loop in the fiber optic cable; forcing the push rod upward, while the loop formed in the fiber optic cable is maintained; rotating the slide arm so that the fiber optic cable loop former is rotated toward the chemical bath; and lowering the slide arm on the vertical column a predetermined height so that the loop formed in the fiber optic cable is provided in the chemical bath to remove a predetermined length of coating from the fiber optic cable.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.